In this competing continuation, we will conduct a longitudinal study (1993-2007) of 96 large metropolitan areas to study trends and predictors of changes in the population prevalence of drug injectors, HIV) prevalence among injectors, and related prevention programs. In stage one of this project, we developed ways to estimate the population density of injection drug use and HIV prevalence rates in metropolitan areas. We showed that per capita injection drug use increased during the 1990s in many localities, including Baltimore and Salt Lake City. HIV prevalence rates among drug injectors increased in Baltimore and some other areas. In many metropolitan areas, drug injection and HIV rates among injectors declined. The extent to which local HIV prevention programs reached drug injectors also varied widely: 3 metropolitan areas provided treatment to 20% or more of their injectors, while 13 areas reached less than 5%. HIV counseling and testing rates also varied widely. In cross-sectional analyses, we showed that local government budgetary decisions, social and economic factors, and drug abuse interventions were related to injection drug users per capita, HIV revalence among drug injectors, and the presence and size of various programs to prevent HIV among drug injectors. We will build upon our existing data and construct a database for these 96 metropolitan areas containing annual estimates from 1993 - 2007 of drug injectors per capita; HIV prevalence, incident AIDS cases and AIDS mortality among drug injectors; program availability and size; socioeconomic conditions, and government budgetary allocations. We will (1) describe patterns of change over time in prevention programs and epidemiology. We will use longitudinal analysis methods to study (2) how changing socioeconomic conditions, epidemiologic need, budgetary constraints and choices, and policy choices are related to subsequent HIV prevention programming; and (3) how all these variables are related to later changes in (a) drug injectors per capita, (b) HIV prevalence and AIDS among drug injectors, (c) drug abuse treatment and other programs for drug injectors, and (d) racial/ethnic disparities in appropriate indicators. We will use these analyses to develop a well-theorized scientific understanding of forces that shape metropolitan area HIV/AIDS epidemics, rates of drug injectors per capita, and prevention programs. The resulting scientific knowledge base can help develop programs and policies so as to avoid epidemics and, if needed, control them.